Well it does depend on where you are, but Marine band is a licenced band. Here in the UK, the rules mean that it's a maritime service, so the vessel has a licence and you as an operator have a licence (and an exam like ham radio). If you are in a marina, you have a couple of channels you can use to talk to the other marina traffic. However - despite having proper callsigns, most people use the vessel name, or their business entity name - so as I do antenna fittings and testing work, my callsign usually is ears mobile, as that's the business name. Apart from the lifeguards who also use callsigns, this means it's rare too hear people on shore. If you are not linked in some way with maritime services, you can't use marine radio with the tests - so somebody buying a marine radio on Ebay cannot legitimately talk to boats without licences, tests and paperwork. Not sure out of England.